TYPO3 Core

In Typo3 4.7.14 (but similarly in earlier versions, starting from about 4.7.7) backend I observe an undesired, faulty behaviour of the main frame (i.e the frame which displays the RTE, etc.):

When I do some more heavy editing (not only adding some lines of text, but rather writing longer texts with various sub-headlines, and other typical RTE formatting), at a certain moment, out of a sudden, the icon bar above (that holds the buttson for "save", "save and close", "save and new", etc.) disappears.

Actually, in terms of html output it is still there (visible in the source code), but it gets hidden by the main content area (that just seems displaced by, say, 50 px, to the top).

In this condition there is no way to hit the "save" button in order to save work done. In the worst case, the work is lost.
(There is one workaround: 2 of the mentioned buttons are visible with exactly 1 pixel not covered by the displaced central area, and with some trial and error, one can touch them and save the text. But is is hard to touch just this one pixel with the mouse.) Another workaround is calling only this frame (Firefox: right klick --> this frame --> display only this frame). Then the buttons are visible, but returning to where one was is difficult afterwards.

I have tried to find out what css formatting might be involved in the bug, but the html structure of the backend is so complex that I did not succeed. (My idea was identifying the css, and when it happens, to assign manually in Firebug, some more top-margin or so.)

A screenshot of the area with the hidden icon bar is included.

I cannot give an exact description when this happens, but
generally it seems to happen when
- texts are longer than the RTE window would keep visibly by default
- Using the line break, paragraph break or backspace key, and there is some line shifting in the RTE window.
- Both writing ordinary text content and writing news in the "News Admin" is affected

Environment were I observed this:
- Firefox (latest version, and previous versions=
- Windows XP
- Typo3 4.7.7 (?) up to 4.7.14 (.12 and .14 definitely)